PROJECT SUMMARY/ABSTRACT The overall goal of this proposal is to establish that the focal region of low shear stress (0-4 dyne/cm2) immediately downstream or in the post-stenotic segment of ICAD is a marker of atherogenesis, providing a therapeutic target for anti-inflammatory or anti-thrombotic interventions. Our central hypothesis is that post- stenotic low shear stress associated with atherogenic endothelial pathophysiology provides a rational basis for precision medicine of ICAD. Our preliminary data on low shear stress in these regions within SAMMPRIS confirm the potential influential role of shear stress associated with endothelial pathophysiology recognized in systemic atherosclerosis, yet extended to the cerebral circulation for the first time. Our three independent specific aims leverage an ongoing, invaluable collaboration and the unmatched quality of the SAMMPRIS data archive. The Neurovascular Imaging Research Core at UCLA will conduct the prospective experiments to validate focal low shear stress measured on CTA CFD of MCA ICAD with detailed anatomical flow models created from the same source images, with co-registered flow measured on 4D MRA [SA-1]. This step enables us to use these validated flow models to directly observe flow vortices and adjacent low shear stress on particle image velocimetry under microscopy [SA-1]. These validated MCA flow models serve as a scaffold for endothelium, where the cell morphology, expression of VCAM-1 and platelet aggregation can be studied [SA- 2]. The clinical relevance of post-stenotic low shear stress (0-4 dyne/cm2) in these 50 MCA lesions will be corroborated via comparison with CTA CFD of the contralateral homologous segment [SA-3]. Associations of this clearly defined potential therapeutic target of post-stenotic low shear stress will be examined with respect to other clinical variables and subsequent neurological outcomes in SAMMPRIS [SA-3]. These observations will be similarly conducted across all 140 SAMMPRIS CTA CFD subjects to investigate the generalizability of non-invasive CTA CFD in other arterial lesion sites [SA-3]. All image post-processing, CTA CFD, 4D MRA, 3D printing and biological assays of endothelial pathophysiology will be conducted at UCLA, where we have pioneered this workflow. The collaboration and guidance of the WASID and SAMMPRIS trial leadership is an important element of this new approach to ICAD that employs the statistical expertise at Emory of these landmark trials and their detailed imaging and clinical analyses. Our extensive preliminary work reflecting collaborative expertise on a novel imaging and biological framework, coupled with intensive experience linking the SAMMPRIS imaging and clinical datasets, provide a logical extension of knowledge on atherogenic low shear stress into the cerebral circulation.